A dramatic seaweed invasion has hit coastlines across Florida and the Caribbean, killing wildlife

Shorelines around Florida and the Caribbean have been choked with invaders over the past month. No, it’s not tourists — it’s seaweed.

Sargassum seaweed, which originates in the Gulf of Mexico and is actually a type of algae, has been washing up on beaches and coastlines in vacation-heavy hotspots like Miami and Cancun since July.

The weeds have wreaked havoc on local fauna, choking coral reefs and destroying habitats for birds, sea turtles, and fish. The seaweed deluge has also made life difficult for fisherman, since it is capable of wrecking boat propellers, fishing nets, and engines.

Sargassum seaweed is usually pushed by currents into the Sargasso Sea — a large gyre off the coast of North America — where the floating mats serve as an important habitat for marine organisms.

Researchers are struggling to figure out why the weeds have started washing up on Caribbean coastlines. Some experts say the influx of Sargassum could be fueled by a combination of increased nitrogen pollution from agricultural runoff and rising ocean temperatures, according to The New Republic.

The first Sargassum invasion in the Caribbean was recorded in 2011, according to the BBC.

In some extreme cases, resorts have had to close beaches during the busy summer season to remove the seaweed. Here’s what the invasion looks like:

Sargassum algae is pictured along Punta Piedra beach in Tulum, Mexico on August 11, 2018. REUTERS/Israel LealThe most recent invasions began in July, and experts say they may last through September.

A boat floats on the water, surrounded by Sargassum in Bahia La Media Luna, Mexico on August 5, 2018. AP Photo/Eduardo Verdugo

The island of Barbados declared a national emergency in August because of the seaweed invasion.

The seaweed can pile up to 7 meters thick (over 22 feet) on coastlines.

Sargassum washes along the shores of Sunny Isles Beach in South Florida on July 11, 2018. AP Photo/Brynn Anderson

“We’ve had mass mortality of sea turtles that have gotten trapped under ever-thickening piles,” Hazel Oxenford, a Barbados-based fisheries biologist at the University of the West Indies, told The New Republic. “When the turtles try to come up for air, they drown.”

In its natural habitat in the Sargasso Sea, the floating algae provides a habitat for fish and crustaceans, which seabirds and sharks then feed on.

Researchers struggling to understand these Sargassum blooms have said more research is needed, especially into the role of nitrogen pollution and ocean acidification.

Beachgoers make their way through seaweed on Wednesday, July 11, 2018, in Sunny Isles Beach, Florida. AP Photo/Brynn Anderson

“The issue is that we never know what it’s going to be like — we can have a week or two weeks where it’s very clear and then all of a sudden overnight it washes in,” Larry Basham, chief operating officer of Elite Island Resorts, told the BBC.

Children play on the beach full of Sargassum in Bahia La Media Luna, Mexico on August 5, 2018. AP Photo/Eduardo Verdugo

“It’s yet another man-made problem that’s been thrown at the Caribbean that isn’t our doing,” Oxenford told The New Republic.